Hyperpolarized Xenon (129Xe) is becoming the contrast agent of choice in a broad spectrum of diagnostic protocols. Specifically, hyperpolarized 129Xe offers extraordinary potential as a contrast agent for magnetic resonance imaging (“MRI”).
129Xe is hyperpolarized by spin-exchange optical pumping using a gas mixture of Xe (with natural abundance of 129Xe or enriched in 129Xe), a quenching gas (nitrogen or hydrogen), and optional buffer gas (typically helium). In addition to these gases, the flowing gas mixture acquires a vapor of alkali metal during the polarization process. 129Xe comprises only a fraction of the total gas mixture.
The system of hyperpolarizing uses a polarizing cell, polarized laser light, and a magnetic field. The polarizing cell has at least a pair of openings defining an entrance and exit to allow a flowing gas mixture into and out of the polarizing cell. The laser is positioned to allow laser light to enter through a transparent window into the polarizing cell, most beneficially in a direction opposite the flow of the gas mixture. The magnetic field is oriented along (or against) the direction of laser propagation.
A number of steps are involved in hyperpolarizing 129Xe. The first step requires moving a flowing mixture of gases through the polarizing cell, the gas at least containing 129Xe and containing (or acquiring) the vapor of at least one alkali metal. The second step is propagating circularly polarized laser light through the polarizing cell such that it illuminates the flowing gas mixture. The final step is immersing the polarizing cell in a magnetic field. These steps can be initiated in any order, although the gas entering and then leaving the cell, the propagating laser light, and the magnetic field immersion must be concurrently active for polarization to occur and be made available for beneficial uses.